1. Field of Invention
The present invention relates to signal transmission structure. More particularly, the present invention relates to a signal transmission structure which comprises a circuit board and a coaxial cable connector.
2. Description of Related Art
On the large-scale printed circuit board (PCB) and the packaging substrate, the signal lines between two nodes or between two ends are electrically connected while maintaining a consistent wire width, so that the characteristic impedance of the signal wire can be maintained constant while the electric signal is transmitted via the signal lines. And, especially in transmitting the high-speed and high-frequency signals, the two ends require a better impedance-matching design to reduce the reflection resulted from the impedance mismatch; that is, to reduce the insertion loss and relatively increase the return loss when the signal is transmitting, so as to reduce negative impact upon the quality of transmitting signal.
FIG. 1A is a top view of a conventional upright SMA (Sub-Minature type A) connector assembled to a circuit board, and FIG. 1B is the top view of the circuit board in FIG. 1A. FIG. 1C and FIG. 1D are the cross-sectional views of line A-A′ and line B-B′ of FIG. 1A, respectively. Referring to FIG. 1A to FIG. 1D, the conventional circuit board 100 has a signal through hole 100a and a plurality of alignment Through holes 100b; wherein, the signal through hole 100a and these alignment through holes 100b all extend through the conventional circuit board 100. Additionally, the conventional circuit board 100 also has a plurality of alignment hole pads 116, a signal hole pad 112, and a signal trace 114 connected to one of the signal hole pads 112 on a surface thereof. The signal hole pad 112 surrounds the signal through hole 100a, and the alignment hole pads 116 surround the alignment through holes 100b respectively. Additionally, the conventional circuit board 100 also has a internal reference plane 120 (FIGS. 1C, 1D), which can be a ground plane or a power plane; wherein, these alignment hole pads 116 are electrically connected to the internal reference plane 120.
The conventional upright SMA connector 200 is also a coaxial cable connector, and the conventional upright SMA connector 200 is disposed on the circuit board 100. The conventional upright SMA connector 200 has a signal pin 210 and a plurality of alignment pins 220, wherein the signal pin 210 is inserted into and soldered to the signal through hole 100a, and the signal pin 210 is electrically connected to the signal hole pad 112. Therefore, the signal from the conventional upright SMA connector 200 can transmit to the signal trace 114 via the signal pin 210 and the signal hole pad 112 in sequence. Additionally, these alignment pins 220 are inserted into and soldered to the signal through holes 100b, and these alignment pins 220 are electrically connected to these alignment hole pads 116. Using the same method, these alignment pins 220 can be electrically connected to the internal reference plane 120 via these alignment hole pads 116.
The relatively larger signal pin 210 (the diameter of the signal pin 210 is 1 mm, for example as seen in FIG. 1C) requires a relatively larger signal hole pad 112 on the circuit board 100, however, the relatively larger signal hole pad 112 may induce relatively serious parasitic capacitance effect. In other words, the transmission quality may be diminished due to the derived high capacitance of the signal pin 210 when the signal is transmitted from the signal pin 210 to the signal hole pad 112. Additionally, as the extending part of the signal pin 210 passing through the circuit board 100 creates parasitic capacitance, the quality of the signal transmission may further diminish. Note that the quality of the signal transmission may be more seriously degraded when the signal transmitted byte signal pin 210 is of high-frequency signal.